Medical electrodes have, in the past, taken many shapes and forms. Principally, they have been shaped according to the use for which they are intended. Electrodes used with monitoring apparatus, such as EKG and EEG machines, commonly have small round contact surfaces, whereas electrodes used with such stimulation apparatus as pain control devices tend to be larger and have rectangularly, circularly and other conveniently shaped contact surfaces. Whether intended for monitoring or stimulation use, a design objective for each electrode group has been, and continues to be, good electrical signal transmission between a patient's skin surface and the electrical cables connected to a particular piece of apparatus. With respect to stimulation and monitoring electrodes, efficient signal transmission across the epidermis conductor interface is desirable. Further, with respect to stimulation electrodes, effective signal transmission free of current concentration points or "hot spots" is also desirable.
Of the electrodes presently available, many offer combination structures including a metallic or otherwise conductive support member to which an electrical wire from an associated apparatus may be attached.
Certain of the currently available electrodes, including electrical stimulation electrodes are disclosed in U.S. Pat. Nos. 4,722,354; 4,736,752; 4,819,328; 5,038,796 and 5,450,845 to Axelgaard et al which are hereby incorporated by reference to show various electrode designs including but not limited to medical electrode shapes, structures, materials and means and methods for connecting said medical electrodes to the appropriate electrical apparatus.
In many instances, the medical electrodes of the prior art need the addition of generous amounts of an electrode paste or gel applied directly to the conductive support member to enhance conductivity across the skin-electrode interface to the point where acceptable operating conditions are achieved.
The prior art electrodes that require an electrode paste or gel or electrolyte solution provide a structure which does not always maintain constant, efficient and effective electrical transmission for long periods of time without the need for additional electrode paste, gel or solution. Moreover, there is a tendency while using these electrodes, for the electrode gel to separate and/or to flow to a non-uniform thickness. Under these conditions, sections of the conductive support member could be exposed to the skin and local hot spots can result which can cause discomfort if not severe enough to cause burns to the patient's skin. Therefore, medical electrodes wherein the adhesive, itself, provides the conductive interface between the skin and the electrical connector are very desirable. An electrode of this type is disclosed in U.S. Pat. No. 4,066,078 to Berg. In this patent, the polymer itself acts as the adhesive and, through the quaternary groups attached to the polymer backbone, provides a conductive interface.
Nevertheless, others have continued to formulate adhesive materials that effectively adhere to the skin. For example, materials that can be utilized in fabricating a medical electrode and also provide adequate conductivity are referenced in U.S. Pat. Nos. 4,830,776; 4,274,420; 4,777,954; 4,699,146; 4,458,696; 5,024,227; 4,243,051.
Copending U.S. patent application Ser. No. 08/603,635, now U.S. Pat. No. 5,868,136, provides an electrode with an improved electro-conductive skin-interface substrate, which will perform a similar function to, and eliminate the need for, an electrolyte solution, electrode paste or electrode gel. This patent is to be totally incorporated by this reference to show suitable materials useful in the present invention. However, conductive adhesives and/or gels heretofore developed offer compromise properties such as, for example, peel strength which may be suitable for permanent adhesion to a conductive member but accordingly do not offer or facilitate repeated removal and contact with a patient's skin.
In addition, heretofore manufacture of conductive gel electrodes has included separate handling of the gel before application to a conductive member. Because of the poor strength of the gels, a scrim is often embedded into the gel in order to enable handling of the gel and its application to a surface of a conductive member. If a scrim is not used, the gel may stretch or distort during handling which results in an uneven layer of gel or the conductive member. This results in poor and/or unreliable current densities provided by the electrode.
However, the use of a scrim in prior art electrodes introduces yet another problem. That problem is accurate placement of the scrim within the gel. Currently, a scrim is introduced into the gel upon extrusion of the gel into a layer. In this procedure accurate placement within the gel layer has proved to be very difficult since the scrim tends to float or sink within the gel before curing or setting thereof.
It should be appreciated that if the scrim ends up too close to the gel surface facing the conductor, delamination occurs and if the scrim ends up too close to the gel surface contacting a patient's skin, causes inadequate adhesion, often resulting in partial or full separation of the electrode from the skin.
In accordance with the present invention, an electrode is provided with a multilayer substrate that has very good skin characteristics such as softness, wetness and readhesion, while at the same time having excellent permanent adhesion to a conductive member.
In addition, when a scrim is desirable, the method of the present invention enables accurate placement thereof within the multilayer gel so as to eliminate all prior problems, hereinabove discussed, with regard to the use of such scrims. A further feature of the present invention includes the structure enabling accurate incorporation of a physiologically active agent or ions, for iontophoresis in a more economical and efficacious way than the prior art.
Yet, another feature of the present invention is the use of conductive layers having widely different adhesivity or specificity to widely different substrates. As will be set forth herein, this enables an electrode to be used in combination with a garment in which the electrode slides over a patient's skin.
Other objects and advantages of the present invention will become apparent from a careful reading of the specification below.